Air-cooled power converter, drive device for rolling stands, and power converter system

ABSTRACT

An air-cooled power converter with gate turn-off power semiconductors, is described in which the cooling capacity is such that the temperature of the gate turn-off power semiconductor does not exceed a critical temperature limit, the power converter having optimized heat sinks, at least some of which are thermally connected in parallel, and the power converter is designed to operate at a continuous load of 1 to 20 megawatts, preferably of 2 to 10 megawatts.

FIELD OF THE INVENTION

The present invention concerns an air-cooled power converter with a gateturn-off.

BACKGROUND INFORMATION

Water-cooled megawatt power converters are known. However, conventionalpower converters are expensive to manufacture and maintain.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a power converter in acapacity range of 1 to 10 MW that can be manufactured moreadvantageously compared to the conventional power converters. It isparticularly desirable that a power converter in the capacity range of 1to 20 MW be provided, which is easier and less expensive to operate andmaintain than conventional power converters.

Air cooling for power converters operating in the range of 1 to 20 MW isconsidered unsuitable by experts in the field. It has, however, beenshown that power converters in the above-mentioned capacity range withair cooling are feasible. Such air-cooled power converters have provento be particularly cost-effective and require little maintenancecompared to known water-cooled power converters.

In an advantageous embodiment of the present invention, heat sinkselectrically connect gate turn-off power semiconductors. This electricalconnection also represents a good heat connection, so that the heatgenerated in the power semiconductors is sufficiently dissipated. It hasalso proven to be advantageous to use heat sinks with such a high heatcapacity that they react inertially to peak loads.

In another advantageous embodiment of the present invention, the powerconverter has a fan that supplies ambient air or pre-cooled air to theheat sinks or that advantageously draws ambient air through the heatsinks.

Other advantageous and inventive details are presented in the followingdescription of the embodiment with reference to the drawing and inconjunction with the subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a motor supplied by a power converter with a diode powerrectifier on the line side;

FIG. 2 shows a motor supplied by a power converter with aself-commutated power rectifier and power inverter also on the lineside;

FIG. 3 shows a power converter arrangement with an automation deviceconnected via optical fibers;

FIG. 4 shows a three-point power inverter with GTO thyristors (maincircuit without RC circuit);

FIG. 5 shows a three-point power inverter with RC GTOs and RC circuit;

FIG. 6 shows a power converter arrangement for supplying a three-phasemotor with a three-point power converter section on the line and loadside;

FIG. 7 shows a power converter arrangement for double-sided supply of athree-phase motor having an open winding with a three-point powerconverter section;

FIG. 8 shows the mechanical construction of a power converter accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a motor 15 supplied by a power converter with a diode powerrectifier 2 on the line side. The power converter arrangement ispreferably designed as a series connection of two B6 diode bridges. Theline-side connection is implemented using a transformer 1 with twosecondary winding systems preferably electrically offset by 30° toachieve a 12-pulse phase effect. Diode power rectifier 2 is connected tothe load-side power inverter 4 via voltage link 3 on the dc side. Thevoltage link is preferably connected across three poles—the positivelink pole, the negative link pole, and the dc neutral. Load-side powerinverter 4 is designed as self-commutated three-point power inverter towhose output three-phase motor 15 is connected using three conductors.

FIG. 2 shows a motor 9 supplied by a power converter withself-commutated power rectifier 6 and power inverter 8 on the line side.The power converter arrangement has a line-side self-commutated powerrectifier 6, connected on the dc side to load-side power inverter 8 viavoltage link 7. Both power converter sections 6 and 8 have a three-pointdesign, and the voltage link is preferably connected via three poles—thepositive link, the negative link, and the DC neutral. Load-sideself-commutated power rectifier 6 is connected to the line viatransformer 5. The circuit is preferably of the same design as that ofload-side power inverter 8 and allows operation both as a powerrectifier and as a power inverter for energy recovery, for example inbraking motor 9. The output of load-side power inverter is connected tothe three-phase motor via three conductors.

FIG. 3 shows a power converter arrangement with an automation device 14for controlling power converter 16, the entire information exchangetaking place over an optical fiber connection 13. Power converter 16 hasa line-side power converter section 10, a voltage link 11, and aload-side power converter section 12. The power connections of the powerconverter sections with the line and the motor can be implemented asshown in FIGS. 1 and 2, for example. Power converter 10 contains all thesensors required for operation and monitoring, so that no other outsideconnections are needed. It is not shown that both the power converterand the automation device require an auxiliary power supply or abattery.

FIG. 4 shows the main circuit of a three-point power inverter.Positive-side link capacitor 54 and negative-side link capacitor 55 areconnected in series between positive DC pole 56 and negative DC pole 57.Their point of connection forms DC neutral point 58. Phase modules 50,51, 52, each with four GTOs connected in series and free-wheeling diodesconnected in anti-parallel, are connected between the positive andnegative DC poles. The point of connection between the first and secondGTOs of a phase module and the third and fourth GTO of a phase module isconnected to two additional diodes connected in series and inanti-parallel to the GTOS; the neutral point of these two diodes isconnected to DC neutral point 58. The point of connection between thesecond and third GTO of a phase module forms the respective outputterminal connected to motor 53.

FIG. 5 shows a three-point power inverter component with RC GTOs and RCcircuit. The series connection of an inductance L1, four RC GTOs(reverse conducting gate-turn-off thyristors) V1, V2, V3, V4 andinductance L2 between the positive DC pole 24 and the negative DC pole26 form together with the two neutral point diodes V15 and V16 the maincircuit of a phase module of a three-point power inverter. The anode ofV15 is connected to DC neutral point 25 and its cathode is connected tothe connection point of first RC GTO Vl with second RC GTO V2. Thecathode of X16 is connected to DC neutral point 25 and its anode isconnected to the connection point of third RC GTO V3 with fourth RC GTOV4. The connection point between the second RC GTO V2 and the third RCGTO V3 forms the ac output of phase module V (V or W).

L1 and L2 are used to limit the current rise rate; RC circuits V21 andV22 with C7 and C1, as well as V24 and V23 with C17 and C11 are used tolimit the voltage rise rate when switching the GTOs. The energy storedin the respective RC circuits in each switching operation is convertedinto heat at resistors R3 and R4 and the overcharging of capacitors C1and C11 is prevented or reversed.

The two RCD protection circuits R11, C9, V25 and R21, C19, V26 are usedas additional protection of the two middle RC GTOs V2 and V3. They areadvantageously used in high-capacity power converters with the resultinglarge physical dimensions for preventing voltage surges indesign-related parasitic inductances of GTOs V2 and V3.

FIG. 6 shows a power converter arrangement for supplying a three-phasemotor with the line-side power converter section 33 and load-side powerconverter section 34 having the same three-point design with GTOs. Themain circuit of each phase module is illustrated with their respectiveRC circuits 40 and 41. Positive-side link capacitor 37 forms, togetherwith negative-side link capacitor 39, the DC voltage link, over whichthe two power converter sections are connected. The positive-side RCcharge reversal resistor 36 and the negative-side RC charge reversalresistor 38 are connected to the respective sides of RC circuits 40 and41. The output of line-side power converter section 33 is connected toline 30 via transformer 31 and circuit breaker 32. The output ofload-side power converter section 34 is connected to three-phase motor35.

In the arrangement of FIG. 7, the output of a first power converter 74and the output of a second power converter 75 are connected to a side 71and 72, respectively, of the open three-phase winding of three-phasemotor 73. With this arrangement, a particularly advantageous operatingcondition is achieved in addition to doubling the capacity, since, asassumed according to the tuned pulse method, a largely sinusoidalcurrent is achieved in the motor with low harmonics even at lowswitching frequencies.

On the line side, first power converter 74 is connected to power supplyline 60 via an optional line-side additional inductance 63 and a firststar/delta connected transformer 61, for example. The second powerconverter 75 is connected to power supply line 60 via an optionalline-side additional inductance 64 and a second transformer 62,preferably electrically offset with respect to the first transformer by30° (e.g., star/star connected). With this arrangement, particularlyadvantageous line reaction conditions are obtained, especially when, asin the present example, the power converter is composed of three-pointconnected power converter sections. Even at a fundamental component loadof the self-commutated line power converter, a sinusoidal current isobtained with very little harmonics.

The two power converters 74 and 75 have line-side power convertersections 66 and 65 and load-side power converter sections 69 and 70,respectively, each of which is connected via DC voltage link 67 and 68,respectively. The two DC voltage links 67 and 68 are electricallyinsulated from one another. All power converter sections 66, 65, 69, 70are three-point connected, preferably with RC GTOs.

FIG. 8 shows the mechanical construction of an air-cooled powerconverter according to the present invention. The semiconductor elementsare mounted in this embodiment on a pull-out power rectifier module 81.Power rectifier module 81 can be inserted into a support 82. Support 82is shown in FIG. 8 without side walls or doors. The unit is cooled usingan air current generated by fan 80 and blown through support 82 andinserted power rectifier module 81. The semiconductors of powerrectifier 81 are preferably arranged between heat sinks 83, which arealso cooled by the air stream.

What is claimed is:
 1. An air-cooled power converter, comprising: gateturn-off power semiconductors; and heat sinks cooling the gate turn-offpower semiconductors and having an optimized design, at least some ofthe heat sinks being thermally connected in parallel, wherein a coolingcapacity of the power converter prevents a temperature of the gateturn-off power semiconductors from exceeding a predetermined criticaltemperature, and wherein the power converter operates at a continuousload of between 1 megawatt and 20 megawatts.
 2. The power converteraccording to claim 1, wherein the continuous load is between 2 megawattsand 20 megawatts.
 3. The power converter according to claim 1, whereinthe heat sinks electrically connect individual ones of the gate turn-offpower semiconductors.
 4. The power converter according to claim 1,wherein the power converter responds inertially to load peaks due to aheat capacity of the heat sinks.
 5. The power converter according toclaim 1, further comprising: a fan one of supplying ambient air to theheat sinks, supplying a pre-cooled air to the heat sinks, and drawingambient air through the heat sinks.
 6. The power converter according toclaim 1, further comprising: a DC voltage link.
 7. The power converteraccording to claim 6, further comprising: a three-point connected DCvoltage link.
 8. The power converter according to claim 7, furthercomprising: an n-point connected power converter, wherein n is equal toor greater than
 5. 9. The power converter according to claim 1, furthercomprising: a current link. 10.The power converter according to claim 1,wherein the power converter is a direct power converter.
 11. The powerconverter according to claim 1, wherein the gate turn-off powersemiconductors include gate turn-off thyristors.
 12. The power converteraccording to claim 1, wherein the gate turn-off semiconductors includeMOS-controlled thyristors.
 13. A drive device for rolling stands,comprising: gate turn-off power semiconductors including insulated gatebipolar transistors; heat sinks having an optimized design, at leastsome of the heat sinks cooling the gate turn-off power semiconductorsand being thermally connected in parallel; wherein a cooling capacity ofthe drive device prevents a temperature of the gate turn-off powersemiconductors from exceeding a predetermined critical temperature, andwherein the power converter operates at a continuous load of between 1megawatt and 20 megawatts.
 14. The drive device according to claims 13,wherein the gate turn-off power semiconductors are reverse-conducting.15. The power converter according to claim 1, wherein the powerconverter operates at a shock load of between 2 megawatts and 30megawatts.
 16. The power converter according to claim 15, wherein theshock load is between 4 megawatts and 20 megawatts.
 17. A powerconverter system, comprising: two power converters, each of the twopower converters including gate turn-off power semiconductors and heatsinks cooling the gate turn-off power semiconductors, at least some ofthe heat sinks being thermally connected in parallel, wherein a coolingcapacity of each of the two power converters prevents a temperature ofthe gate turn-off power semiconductors from exceeding a predeterminedcritical temperature, and wherein each of the two power convertersoperates at a continuous load of between 1 megawatt and 20 megawatts;and an electric motor connected to the two power converters in tandem,the electric motor including open windings and being supplied with powerby the two power converters, a first one of the two power converterssupplying the power from a first side of the electric motor, a secondone of the two power converters supplying the power from a second sideof the electric motor.
 18. The power converter according to claim 1,wherein the power converter is designed as a fuseless power converter.19. The power converter according to claim 1, wherein the powerconverter supplies an electric motor, the electrical motor being used inone of a rolling mill of a shipyard, an electric vehicle and a linecompensation.